The Animal House – The Incredible Termite Mound

The Animal House – The Incredible Termite Mound

While some termites live in the wood of our homes, others build their own houses, some of the most impressive structures in the animal world. Their mounds are forever-evolving cities, made from the simplest materials. Working independently, without any coordinator or blueprint to reference, they construct temperature-controlled environments that include elaborate ventilation and cooling systems, and specialized chambers that store food, contain fungal gardens, hold eggs, and house the egg-producing queen. As a colony, they are able to create worlds that far exceed their individual capabilities.

    The mound is constructed out of a mixture of soil, termite saliva and dung. Although the mound appears solid, the structure is incredibly porous. Its walls are filled with tiny holes that allow outside air to enter and permeate the entire structure.

The top of the mound consists of a central chimney surrounded by an intricate network of tunnels and passages. Air travels through the porous walls into a series of small tunnels until it reaches the central chimney and rises up. When fresh air mixes with this warm air, the air cools and sinks down into the nest. This ventilation system constantly circulates the air and ensures that oxygen reaches the lower areas of the mound and keeps the nest from overheating.

Termites do not live throughout the mound but spend most of their time in a nest located at or below ground level. It’s comprised of numerous galleries separated by thin walls. Workers are constantly repairing areas that require maintenance and adding new tunnels and corridors to the nest.

A city of termites requires a lot of food, and the mound has many storage chambers for wood, the insect’s primary food source. Termites also cultivate fungal gardens, located inside the main nest area. Termites eat this fungus which helps them extract nutrients from the wood they consume. Maintaining the fungal gardens takes precise temperature control, and the remarkable architecture of the mound keeps the temperature almost constant.

The queen and king reside in the royal chamber. The queen’s sole purpose is to produce new termites to help build and protect the nest. Incredibly, the queen can produce thousands of eggs a day and live for up to 45 years, during which time she will grow to the point where she is unable to move. Workers carry her eggs to a special nursery where they are fed on compost until they turn into adults.

At the base of the mound are several openings that the termites use to enter and exit the nest. Termites make forays out to collect food at night, when temperatures are cooler.

  • Six feet below ground level is the cellar. It’s the coolest part of the structure. Its ceiling is comprised of a series of thin plates that absorb moisture from the colony above and provide another ingenious cooling mechanism. As the moisture evaporates, the temperature falls, cooling the air around the nest.

    Collective Mind in the Mound: How Do Termites Build Their Huge Structures?

    Termites move a fourth of a metric ton of dirt to build mounds that can reach 17 feet (5 meters) and higher.

    PUBLISHED August 1, 2014

    For the past 26 years, J. Scott Turner has filled termite mounds with propane, scanned them with lasers, and stuffed them with plaster. He has fed microscopic beads to termites, given the insects fluorescent green water, and even tried to turn termite behavior into a video game.

    A professor of animal physiology at the SUNY College of Environmental Science and Forestry in Syracuse, this rangy intellectual MacGyver does it all in search of clues to a biological mystery: How do tiny termites build such spectacular structures?

    A single termite can be barely bigger than the moon of a fingernail, its semi-transparent exoskeleton as vulnerable to sunlight as to being crushed by a child in flip-flops. But in groups of a million or two, termites are formidable architects, building mounds that can reach 17 feet (5 meters) and higher. The 33 pounds (15 kilograms) or so of termites in a typical mound will, in an average year, move a fourth of a metric ton (about 550 pounds) of soil and several tons of water.

    The termites also “farm” a symbiotic fungus that occupies eight times more of the nest than the insects do. And some termites eat as much grass each year as an 880-pound (400-kilogram) cow.

    Like ants, bees, and other social insects, termites live in societies where the collective power of the colony far outstrips that of the individual. Being part of a super-organism gives the tiny termite superpowers. But a termite mound is like a construction site without a foreman—no one termite is in charge of the project. Is there a “collective plan” encoded in the collective mind of the colony? That question has obsessed Turner for years.

    In addition to experimenting in the mounds, Turner designs computer simulations to explore deeper patterns in termite behavior. It wouldn’t be wrong to say he’s been searching for the psyche of the super-organism, but it wouldn’t fully get at the richness of all of the other things he’s noticed along the way—including clues to how humans might build more energy-efficient buildings, how we might design robots to build on places like Mars, and even peculiar termite behaviors that might help us understand how our own brains work.

    Termites communicate with each other using touch and vibrations.

    Photograph by Mark W Moffett, National Geographic

    Always Ready to Rebuild

    Turner pursues his fieldwork amid the semiarid savannas of northern Namibia, on a government-owned research station named Omatjenne—the word for lightning in the local Herero language. Sure enough, on an afternoon tour of the farm, the horizon is loaded with fat, dark clouds that are soon gashed by electricity.

    The life of the termite is a race against rain, Turner says. Termite mounds can take four to five years to build, but a really heavy downpour might cause a third of the mounds to collapse. So termites are always scurrying to rebuild their mounds as fast as the weather erodes them.

    To demonstrate the rebuilding process, Turner uses an auger, a tool that looks like a big corkscrew, to cut into the rock-hard surface of a mound. As he pulls a six-inch (15-centimeter) plug of dirt from the side, termites pour out of the hole. Soldiers fan out with their pinching mandibles ready for battle, and workers with mouths full of dirt run to plug the hole. How do they know there’s a hole in the mound?

    Termites are “novelty detectors,” attuned to excitement and always on alert, says Turner. (When there isn’t external stimulation, termites sometimes stand in little clusters, massaging each other’s antennae.) Experiments in Turner’s lab suggest they respond to slight air movements and changes in humidity and concentrations of gases like carbon dioxide.

    At the first sign of a disturbance, a termite runs to communicate the news with touch and vibrations. Roused, masses of termites fill their mouths with dirt and head toward the source of the problem. The commotion attracts more termites with more dirt, and within an hour or so the hole is patched.

    Scott Turner peers into a plaster cast of a termite mound to ponder its architecture.

    Photograph by Mark W. Moffett, National Geographic

    Peering Inside

    The only way to get a glimpse of the termite super-organism in action is to rip the side off a mound. And so one morning Turner, along with entomologist Eugene Marais of the National Museum of Namibia, takes a backhoe to the test fields. With a single swoop, the backhoe removes the top of a mound and then precisely dismantles the rest, like pulling the walls off a dollhouse.

    The termites are not happy that their walls have suddenly disappeared, and they swarm frantically around the exposed structure. Marais dislodges a chunk of dense soil about the size of a squashed soccer ball—the queen’s chamber.

    After repeated blows of a hand pick, the capsule breaks open suddenly, revealing a saucer about five inches (almost 13 centimeters) across containing the queen. Her sweating body is swollen to the size of a human finger. A coterie of workers carries the eggs she produces—at the staggering rate of one every three seconds—to nearby nurseries, while others feed and clean her.

    The queen herself, once a relatively normal size, retains her original legs, but they are now nearly useless. Her pale body pulsates, the caramel-colored fats and liquids inside swirling under her skin.

    The title “queen” leads people to imagine that she is in charge of the mound, but this is a misconception. “The queen is not in charge,” says Marais. “She’s really a slave.” The queen is the epitome of the super-organism: one for all and all for one. She is a captive ovary, producing hundreds of millions of eggs over her life span of up to 15 years to populate the mound.

    Termites rebuild their mounds with mouthfuls of dirt when they’re damaged or the weather erodes them.

    Photograph by Mark W. Moffett, National Geographic

    Farming Fungus

    Below the queen’s chamber lies the super-organism’s largest organ: the fungus garden. In a symbiotic relationship dating back millions of years, the termites exit the mound through long foraging tunnels and return with their “intestines full of chewed grass and wood, which they defecate upon their return, and other workers assemble these ‘pseudo-feces’ into several mazelike fungus combs,” Turner explains.

    The termites then seed the comb with spores of fungus, which sprout and dissolve the tough cellulose into a high-energy mixture of partially digested wood and grass. For the termites, the fungus functions as a sort of external stomach, but the fungus gets the better deal. Ensconced in elaborate termite-built combs and constantly tended, the fungus receives multiple benefits, including food, water, shelter, and protection.

    In fact, the deal is so lopsided that it calls into question just who’s in charge of the relationship. Collectively, the colony’s fungus accounts for nearly 85 percent of the total metabolism inside the mound, and Turner speculates that the fungus may send chemical signals to the termites that influence—control?—the way they build the mound. “I like to tell people that this may not be a termite-built structure,” he says. “It may actually be a fungus-built structure.”

    The collective power of the termite colony far outstrips that of the individual.

    Photograph by Mark W. Moffett, National Geographic

    Living Quarters

    Which brings us to the most extraordinary organ: the mound itself. Contrary to common notions, termite mounds are not high-rise residence halls. Rather, they are “accessory organs of gas exchange,” in Turner’s words, designed to serve the respiratory needs of the subterranean colony located several feet (a meter or two) below the mound.

    For many years, researchers looked at termite mounds and supposed that the spires worked like chimneys, drawing hot air up and out. But Turner discovered that mounds function more like lungs, inhaling and exhaling through walls that appear impenetrable but are actually quite porous.

    Inside the mound, a series of bubble-like chambers connected to branching passages absorb changes in outside pressure or wind and pass them through the mound. To regulate the mix of gases and maintain a stable nest environment, the termites are forever remodeling the mound in response to changing conditions.

    “A termite mound is like a living thing,” says Turner, “dynamic and constantly maintained.”

    The queen (top right) produces hundreds of millions of eggs over her life span of up to 15 years to populate the mound.

    Photograph by Mark W. Moffett, National Geographic

    Wet Kisses

    While studying termite building behavior, Turner noticed that his subjects seemed to be kissing each other, mouth to mouth, after a complicated ritual that included grooming and begging. Curious, he added fluorescent green dye to their water and discovered that all this “kissing” was actually a bucket brigade, transferring large amounts of water across the mound. A termite can drink half its own weight in water, scurry to a drier part of the mound, and distribute it to other termites. In addition to rebalancing the mound’s moisture level, moving all of this water dramatically changes its shape.

    Turner’s work with termites has attracted some notable collaborators, among them British engineer Rupert Soar. Inspired in part by termite mounds, Soar has plans to build energy-efficient houses with porous walls that make use of passive wind energy. He’s also looked into using termite-style building methods to help robots build structures in remote locations using only local materials.

    Turner added fluorescent green dye to termites’ water to illuminate how they transfer large amounts of water across the mound.

    Photograph by Mark W. Moffett, National Geographic

    Group Brain

    Termites may even change the way we think about thinking. A research project at Harvard’s Wyss Institute for Biologically Inspired Engineering brought computer scientists and roboticists to Turner’s site to observe termite behavior with a range of sophisticated scanners and software.

    Harvard professor of robotics Radhika Nagpal makes an analogy between the behavior of termites and the brain. Individual termites react rather than think, but at a group level they exhibit a kind of cognition and awareness of their surroundings. Similarly, in the brain, individual neurons don’t think, but thinking arises in the connections between them. (Single neurons, for example, may recognize a baseball bat and the smell of hot dogs, but working in concert they let you know you’re at a baseball game.)

    Nagpal’s team set up dozens of experiments to try to observe just where this collective cognition arose. “What program are they running?” mused Harvard physicist Justin Werfel, comparing the termites to robots. “Can we get a stochastic model of a stateless automaton that has no memory but reacts to what it encounters?”

    Nagpal, Werfel, and Kirstin Peterson, also from Harvard, recently used termite behavior as a model to build a small swarm of robots (named TERMES) that assembles a structure without any instructions.

    “This is a system where complexity is of the essence,” Turner says of the termites’ behavior. “If you don’t capture the complexity, there’s no hope of understanding it.” And so the quest continues for the elusive mind in the mound.

    Lisa Margonelli is a senior research fellow at the New America Foundation and the author of Oil on the Brain: Petroleum’s Long, Strange Trip to Your Tank. She is working on a new book about termites.

    How Termites Work

    All social insects have some method for building a home. Honeybees build hives from wax, wasps build paper nests and bees dig tunnels in the ground. All termite species build nests, also known as termitaries or termitaria, but the specifics of these nests can vary.

    Many primitive species build their nests in the food they’re consuming. Scientists categorize these termites according to the type of wood they prefer — damp, rotten or dry wood. In some cases, termites share their homes with fungi and bacteria that destroy wood. Termites often line these nests with particles of soil glued together with saliva, which helps the nests retain moisture and warmth. These colonies aren’t particularly mobile, and when the wood runs out, the colony dies.

    Subterranean termites dig large networks of galleries and tunnels underground. Galleries are used for food storage and for raising larvae. These underground networks give the colony a place to live, and they can connect the colony directly to sources of food, like the roots of decaying trees or the side of a person’s house. If there’s an obstacle between subterranean termites and a food source, they will often build shelter tubes, or extensions of their tunnels. Shelter tubes are usually about the diameter of a pencil, and they’re made of soil glued together with termites’ saliva.

    An underground network of tunnels gives subterranean termites some flexibility in where they live. If the weather gets cold, workers can dig deeper into the soil in search of warmth. The same is true in times of drought. If it gets hot, the colony can move to parts of the nest that are shaded by aboveground structures and vegetation.

    Since they’re concealed in wood or underground, the nests of primitive and underground termites can be hard to locate. Termite mounds are another story. These dome- or tower-like structures can be taller than a person. They are made from particles of soil and termite excrement glued together with workers’ salivary secretions. Some species build mound-like nests on the sides of stumps, trees or poles.

    The typical mound has multiple chimneys and tubes that allow air to circulate through the structure. The inner layers of the mound contain galleries in which the termites live and raise young. The king and queen usually live deep inside the mound, where they are well protected from predators and the elements. Some mound-building termites, particularly those in the subfamily Macrotermitinae, are gardeners. They use underground galleries to grow symbiotic fungi.

    Termite mounds are strong — they can survive fires and floods, although water can enter the inner chambers through the ventilation shafts and drown the termites inside. Concealed nests also offer termites protection from weather and predators. But neither type of nest is invulnerable. Animals like aardvarks, anteaters and pangolins have strong claws that allow them to dig into termite nests. Birds, bats, primates and even people also use termites as a food source. This is one reason why termites play an important part in many ecosystems — they act as food for other animals. Next, we’ll take a look at some of the other ways termites benefit ecosystems.

    Worker termites often feed larvae regurgitated food, much the way birds feed their young. However, the larvae need to develop the ability to digest cellulose on their own — they have to be exposed to the organisms that live in termites’ digestive tracts. This usually requires the larvae to eat other termites’ waste.

    Structure of the termite mound

    The mounds of macrotermitine termites have stereotypical architectures, yet are highly variable in structure.

    All species locate their colonies underground, where they cultivate fungi that aid in cellulose digestion. The mounds enclose a ramifying network of tunnels that forms a respiratory gas exchange system for the nest. Some species may build open chimneys or vent holes into their mounds, while others build completely enclosed mounds that exchange gas through porous thin-walled tunnels (like the Macrotermes mound to the right). Even within populations, the variation of mound structure is prodigious.

    External structure of the Macrotermes michaelseni mound

    Macrotermes mound showing
    elements of
    external mound structure

    A mound that has grown up around a Boscia tree.

    Outwardly, the mound consists of three parts:

    • a columnar spire atop a conical base. The spire reaches on average about 3 meters high, but it can reach as high as 9 meters.
    • a conical base, roughly 4-5 meters in diameter and roughly 1.5 meters tall
    • a broad outwash pediment, roughly 10-20 meters in diameter, consisting of soil eroded from the mound.

    A distinctive feature of these mounds is the northward tilt of the spire. At our study site in northern Namibia, this tilt is about 19 degrees on average, which corresponds to the average zenith angle of the sun (and to the latitude). The spire’s northward tilt is probably due to termites building more avidly on the warmer north-facing surface of the mound (remember that Namibia is in the southern hemisphere). You can read more about this, including a video of how it happens, here.

    Mounds are also often built around trees, as shown here. This may be due to a shelter effect: a foundling colony’s chance of survival to maturity may be enhanced when the founding king and queen land in the shelter of a tree, rather than in the harsher environments between trees. The tree is not harmed by this – indeed it thrives. A curious feature of this association is that termites are often found in association with the tree species that is rarest in this savanna: the Shepherd’s tree, Boscia albitrunca. You can read more about this here. TOP

    Surface architecture

    Patch of new building on mound surface

    Underside of patch of new building revealing egress complex (above) and entrance hole to surface conduit (below).

    The mound surface appears to be solid and impermeable, but it is actually quite porous. The porosity arises from the method that termites employ to grow the mound.

    The mound grows by termites transporting soil onto the mound surface and depositing it there (three videos below of a mound building in the rainy season illustrates this). To get to the surface, termites dig numerous egress tunnels from the surface conduits to the mound surface.

    Notice how the deposition of soil to the surface is episodic. This typically occurs following rainfall events. This is an important clue to why the termites actually build a mound.

    Deposition of new soil onto the surface is evident as patches of moist or rough deposits of soil (right). These new deposits are quite friable and air moves through them with relative ease. These patches of newly deposited soil open directly into the egress tunnels, which is revealed when a patch is removed.

    The mound therefore has a dynamic surface. As soil is eroded from the actions of wind and rain, it is replaced by the action of termites depositing fresh soil. This makes the mound structure malleable, which allows it to be modeled to local conditions.

    The turnover of soil in the mound is seasonal, occuring solely during the rainy season. It is also quite prodigious, amounting to about 250 kg dry mass of soil annually. It is for this reason that these mounds have been likened to slow-motion “soil fountains.”

    Internal architecture

    The relatively simple external architecture masks one of the most sophisticated animal-built structures on the planet. Inside themound is an extensive reticulum of tunnels and conduits, which reveals its function: the mound is an organ of physiology for the termite colony superorganism, which is centered on the underground nest. The nest itself is a spheroidal structure consisting of numerous gallery chambers, each of which contains a fungus comb, where raw forage, such as grass and wood, is digested by the symbiotic fungi (Termitomyces) that the termites cultivate within their nest.

    This network of tunnels is most easily made visible by casting them in plaster and then washing away the soil. The first to do this was the Belgian entomologist Jean Ruelle (below), who cast the tunnel network of a Macrotermes natalensis mound in concrete.

    More recently Rupert Soar (of Loughborough University) and I have cast the internal tunnel network of Macrotermes michaelseni. You can see more about this on the Endocasting page. As in Ruelle’s cast, the tunnel network of the M michaelseni mound consists of an elaborate reticulum of surface conduits (middle) overlying a more extensive reticulum of large-calibre deep tunnels.

    • the egress complexesunderlie sites of active building at the mound surface, and emerge from the vertically oriented surface conduits. At sites of active building, these can be extensive and tortuous. Egress complexes can be found over the entire surface of the mound.
    • the surface conduits run vertically underneath the mound’s outer surface. Egress complexes spout from the surface conduits all along the conduit’s length.
    • The surface conduits also extend below ground to form the paraoecie. This structure envelops the nest, and offers egress from the peripheral chambers of the nest. The paraoecie also merges with the network of foraging tunnels that radiates as far as 70 meters from the nest. The subterranean conduits also connect peripherally with the air spaces of the nest.
    • An amorphous large internal air space, the chimney, extends nearly the vertical length of the mound. The image one conjures is of a large pipe extending from the nest up through the mound. In fact, it ramifies and branches, so that it blends seamlessly into the large network of the mound’s tunnels. Below, it penetrates into the center of the nest, and connects to the nest’s central air spaces, through tiny holes. The chimney is excavated from abandoned fungus galleries.
    • the reticulum is an interweaving network of tunnels that spans the chimney and surface conduits.

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